1. Field of the Invention
The present invention is related to etching techniques, and particularly to a method of controlling ADI-AEI CD difference ratio of openings having different sizes.
2. Description of Related Art
As the requirement of integration level in the integrated circuits gets higher, the dimensions of the circuit pattern gets smaller as well. In the fabricating process of the integrated circuits, the method of reducing the size of patterns mostly utilizes a photolithographic process having high resolution. However, a high-resolution photolithographic process has its optical limitations. Therefore, the technology is very difficult and the fabricating cost thereof is very expensive. Especially for the fabricating process of opening patterns, an after-development-inspection critical dimension (ADI CD) solely related to the photolithographic process is particularly difficult to control. Hence, an after-etching-inspection critical dimension (AEI CD) required by the fabricating process would generally be obtained by adjusting etching recipes. The AEI CD is the size of an opening actually formed in the target material layer.
When openings having different sizes are simultaneously formed in this method, however, the problem that an ADI-AEI CD difference ratio of each of the openings is difficult to properly control still remains. Herein, the so-called “ADI-AEI CD ratio” is defined as: the difference between an after-development-inspection critical dimension and an after-etching-inspection critical dimension. For example, in a process of forming simultaneously a square contact in contact with a source/drain and a share contact in contact with a gate and a source/drain, if a size of the square contact opening is reduced, a size of the larger share contact opening would be reduced even more. When the size of the share contact opening is overly reduced, the share contact subsequently formed would have a resistance so high that an operational speed is greatly lowered. The share contact may even not be able to contact a target gate or a target source/drain region and thereby resulting in a short circuit. In contrast, if sizes of the square/share contact openings are insufficiently reduced, a problem of mistakenly contacting with other elements would occur. Therefore, ranges of size reduction for the two contact openings should both be adequately controlled.
Similarly, in other kinds of opening processes, when various kinds of openings having different sizes need to be formed simultaneously, a range of ADI-AEI CD difference ratio for each type of the openings also needs to be properly controlled simultaneously so as to comply with a range allowed by the fabricating process.